In some London boroughs the number of affordable homes has shrivelled to just a handful. Richmond upon Thames, with a population of 194,000, built just five affordable homes in 2014-15 and the City of London managed zero, while Bromley lost affordable homes after the number of affordable properties was cut when a council estate was refurbished.

In total, 6,856 properties defined as affordable were built in the capital in 2014-15, down from 6,914 the year before. Affordable housing includes shared-ownership properties and homes sold at below conventional market prices.

As a percentage of all housing built in London, affordable housing has fallen to 25%, down from 39% four years ago.

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Siân Berry, Green party candidate for mayor of London, said the statistics published by the GLA – the authority that includes the mayoralty and the London assembly – revealed the extent of the failure to tackle the housing crisis.

She said: “These outrageous figures show that Boris Johnson has been the big developers’ mayor, helping them to push through luxury flats with tiny numbers of genuinely affordable homes.

“I want to kick the developers out of City Hall and bring in the smaller developers and community groups interested in building homes for Londoners, not safety deposit boxes for investors. I would start by restoring the target for half of all new homes to be affordable, and get tougher with developers that aim far lower.”

Haringey in north London was the only council area to see more than half of newly built homes classified as affordable. But the definition of affordability is highly controversial, with some “affordable” homes having a price tag of £873,000, or more than 30 times the average UK wage.

House prices and rents have loomed large in the London mayoral battle, with property costs cited by many voters as their top concern. The Labour mayoral candidate, Sadiq Khan, has called the mayoral election on 5 May “a referendum on housing,” and promises to accelerate the building of genuinely affordable homes. The Conservative candidate, Zac Goldsmith, promises to double homebuilding in the capital to 50,000 a year by 2020.